1. Field of the Invention
This invention relates generally to a protocol for transmitting messages to a group of vehicles and, more particularly, to a protocol for continually transmitting messages to a group of vehicles for a certain period of time and within a certain region in response to a detected hazardous road condition.
2. Discussion of the Related Art
Traffic accidents and roadway congestion are significant problems for vehicle travel. Vehicular ad-hoc network based active safety and driver assistance systems are known that allow a vehicle communications system to transmit messages to other vehicles in a particular area with warning messages about dangerous road conditions, driving events, accidents, etc. In these systems, multi-hop geocast routing protocols, known to those skilled in the art, are commonly used to extend the reachability of the warning messages, i.e., to deliver active messages to vehicles that may be a few kilometers away from the road condition, as a one-time multi-hop transmission process. In other words, an initial message advising drivers of a potential hazardous road condition is transferred from vehicle to vehicle using the geocast routing protocol so that vehicles a significant distance away will receive the messages because one vehicle's transmission distance is typically relatively short.
Warning messages for active safety and driver assistance applications may need to be temporally persistent in nature. In other words, it may be desirable for certain roadway conditions that the warning message be maintained for an extended period of time because of the length of the time the condition may exist, and also to make sure the intended warning is received by all approaching vehicles. For example, an icy patch on a roadway may take several hours to melt, which requires a continuous message to be transmitted to vehicles approaching the hazard area.